FIG. 1 schematically shows a conventional resin deposition pump. The pump is essentially formed of a body 1 provided with an access 2 of admission of resin r from a tank (not shown) and with an access 3 for dispensing a given amount of resin r on a wafer (not shown) rotated for a spin-on deposition. A filtering element 4 masks access 3 inside body 1 to filter the resin r when dispensed. The inlet and dispensing of resin r are controlled by means of an impervious membrane 5 delimiting, within pump body 1, a chamber 6 of resin dispensation and a chamber 7 of control by means of an adapted control fluid, for example, air a. Membrane 5, which is deformable under the action of the control fluid, is generally made of Teflon.
Chamber 7 communicates with a control system (not shown) via a duct 8 on the path of which are inserted valves 9, 10 of air aspiration or injection into chamber 7. A three-way valve can, if desired, replace valves 9 and 10. Accesses 2 and 3 meant for the passing of the resin r can be obtruded through means of respective flaps 11 and 12. Flap 11 associated with admission access 2 is a check valve preventing any sending back of resin r into the tank. Flaps 11 and 12 can be controlled individually by the pump control system, for example, electrically by means not shown, or can be provided with means of elastic return to their respective neutral positions to be controlled by the pressure differences between the inside and the outside of dispensation chamber 6 at the level of accesses 2 and 3.
A cycle of deposition of a determined amount of resin on a wafer comprises at least two steps. It is assumed that chamber 6 is initially filled with resin, that is, a pump initialization cycle consisting of filling chamber 6 from the tank has previously been performed, and that chamber 7 is empty, membrane 5 being against bottom 13 of body 1.
In a first resin dispensation step, air a is injected into chamber 7 via valve 10, valve 9 being closed. The volume of chamber 7 increases and the resulting pressure increase in chamber 6 causes the opening of flap 12 and a dispensation of resin r through access 3, flap 11 being closed during this last step. Air is injected at constant pressure for a given time. The volume of resin r deposited on the wafer thus depends on the time and on the air pressure, set by the control system.
In a second step, the positions (open/closed) of valves 9 and 10 are inverted and air a is aspired from chamber 7. This aspiration causes a volume increase of chamber 6 and the resulting pressure decrease causes the opening of flap 11 and a filling of (chamber 6 from the resin tank, flap 12 being closed. The aspiration goes on until membrane 5 is again against bottom 13.
If desired, the second step is preceded by a step of partial aspiration during which the amount of unused resin r.sub.-- remaining in the pipe connecting access 3 to the area of deposition on a semiconductive wafer is aspired back into chamber 6. The opening delay of flap 11 to enable, during this intermediary step, the return of the undispensed resin r can be obtained by the respective sizing of accesses 2 and 3 and by the opening resistance of flap 11.
A disadvantage of conventional pumps is that filter 4 progressively clogs up during the dispensation cycles. This causes a decrease of the volume deposited on the wafer for a given air injection time.
Now, the volume deposited on each wafer has to be regular from one wafer to another in a same manufacturing series. The user must thus, with a conventional pump, periodically control the deposited volume to adapt the time of the dispensation cycle in the control system, to compensate the pressure increase necessary to maintain a same displacement of membrane 5 to obtain a constant volume deposition.